This invention relates to a turbocharger incorporating a wastegate and wastegate actuator, and in particular relates to the manner in which the actuator is connected to the turbocharger.
Turbochargers are well known devices for supplying air to the intake of an internal combustion engine at pressures above atmospheric (boost pressures), and are widely used in automobiles and commercial vehicles. A conventional turbocharger essentially comprises an exhaust gas driven turbine wheel mounted on a rotatable shaft within a turbine housing. For instance, in a centripetal turbine the turbine housing defines an annular inlet passageway around the turbine wheel and a generally cylindrical axial outlet passageway extending from the turbine wheel. Rotation of the turbine wheel rotates a compressor wheel mounted on the other end of the shaft within a compressor housing. The compressor wheel delivers compressed air to the intake manifold of the engine, thereby increasing engine power.
It is also well known to provide turbochargers with a bypass passageway between the exhaust inlet and the exhaust outlet portions of the turbine housing to enable control of the turbocharger boost pressure. A wastegate valve is located in the passageway and is controlled to open the passageway when the pressure level of the boost air increases to a predetermined level, thus allowing some of the exhaust gas to bypass the turbine wheel preventing the boost pressure from rising further. The wastegate valve is generally actuated by a pneumatic actuator operated by boost air pressure delivered by the compressor wheel.
The conventional pneumatic actuator comprises a spring loaded diaphragm housed within a canister (the wastegate actuator can) which is mounted to the compressor housing. The diaphragm acts on a connecting rod which actuates (typically rotates) the wastegate valve assembly which is mounted in the turbine housing, via a linking lever arm.
The actuator can is connected to the compressor outlet by a flexible hose to deliver boost air to the can which acts on the diaphragm to oppose the spring bias. The spring is selected, and the actuator and wastegate valve initially set, so that under low boost conditions the wastegate valve remains closed. However, when the boost pressure reaches a predetermined maximum the diaphragm is moved against the action of the spring and operates to open the wastegate valve (via the connecting rod and linking arm) thereby allowing some exhaust gas to bypass the turbine wheel.
It is an object of the present invention to provide a new wastegate valve actuator/compressor connection, and a new method of mounting the actuator can on, and connecting the actuator can to the compressor housing outlet.
According to a first aspect of the present invention there is provided a turbocharger comprising a compressor wheel mounted within a compressor housing having a pressurized air outlet, a control valve for regulating the pressure of air supplied from the compressor housing outlet, and pressure operated actuating means mounted to the turbocharger for actuating the control valve, the actuator comprising a case defining a pressure chamber and an inlet for delivering pressure to the chamber, and a substantially rigid connecting pipe of well defined shape extending from the actuator inlet to the compressor housing, the end of the connecting pipe remote from the case communicating with the compressor outlet to deliver pressure to the actuator inlet.
The connecting pipe is preferably integral with, or is secured to, the actuator case so as to form a component of the actuator prior to mounting of the actuator on the turbocharger. The end of the pipe may thus be bought into communication with the compressor outlet simply by appropriate positioning of the actuator when it is mounted to the turbocharger. Alternatively, it would be possible to form the pipe as an integral component of the compressor housing, such that the end of the pipe remote from the compressor housing is bought into communication with the actuator again by the simple process of appropriately positioning the actuator case on the compressor housing when it is mounted to the turbocharger.
According to a second aspect of the present invention there is provided a method of mounting a pneumatic actuator to a turbocharger compressor and connecting a pressure inlet of the actuator to an opening in the compressor housing communicating with the outlet of the compressor, the method comprising:
providing the actuator with a substantially rigid connecting pipe having a well defined shape extending from said pressure inlet; and
mounting the actuator to the compressor housing using mounting means which fix the actuator in a position relative to the compressor housing in which the end of the connecting pipe remote from the actuator communicates with said opening in the compressor housing.
A specific embodiment of the present invention will now be described, by way of example only with reference to the accompanying drawings, in which:
FIG. 1 a partly cut-away perspective view of a turbocharger incorporating the present invention;
FIG. 2 is an enlargement of part of FIG. 1 viewed from a slightly different angle and partly cut-away to reveal details of the wastegate valve and the actuator connection to the compressor housing; and
FIG. 3 is a side view of the turbocharger of FIG. 1 in the direction of arrow A on FIG. 1.